The actual content is not present as an HTML element, it's inside a JSON object in <article ... data-z="...">. In order to show it, one would need to create the corresponding HTML in a script. Although it's doable, I think it's much easier to just view the site in incognito window as it seems to show all answers.
brainly.com , 'free' homework assistance. Change hidden attributes
This site purports to be free to view answers. The answers are indexed by search engines partially or even wholly. An overlay is used to hide answers.
Please remove this frippery for actual free access.
example question
https://brainly.com/question/857387
__test account
email: cretinous
password: 4Circumvention
body class="mint logged-in us js-question-page-with-verified-answer"
href="#main-content" class="visually-hidden" tabindex="-1"
I could not craft uBlock Origin rules to remove & show FREE content.